1. Field of the Invention
The present invention relates to an integrated electronic device with solid-state relay and pre-charge circuit. The invention also relates to a method for connecting/disconnecting two terminals, with pre-charge functions using such a device.
In particular, but not limited thereto, the invention relates to a solid-state electronic relay which can be used for electrically disconnecting/connecting a load from/to a battery for electrical or hybrid traction motor vehicles.
2. Description of the Related Art
Electrical systems with direct current power supply are considered, characterized by electrical generators, circuits with low line electrical impedance and loads with high input electrical capacitance, in which the loads may be connected or disconnected in controlled manner by the generators by means of relays or switches. In such systems, a controlled connection event (e.g., the closing of a relay) between a load and a generator, that were previously disconnected, may instantaneously cause a very high current flow. This occurs, for example, if the voltage at the terminals of the load, in disconnection conditions, is significantly different from the voltage supplied by the generator. The situation described above may cause considerable drawbacks to the generator, to the load, to the connection conductors and to the relays themselves.
A situation of this type may occur, for example, in the automotive context in systems for electrical or hybrid traction vehicles equipped with a source of electrical charge or electrical charge storage or battery adapted to store the electrical energy also used for traction. Such systems operate, for example, with power supply voltages equal to, or higher than 48 V (level that is considered high in the automotive context). Motion systems for an electrical or hybrid vehicle generally include a load group, in particular an electrical motor, adapted to generate the motion, driven by means of an inverter, which is electrically connected to a battery pack or battery group for storing the electrical energy. As mentioned, the battery typically has relatively high voltages, e.g., 48 V. The load group has a high input capacitance; the battery and load group are connected/disconnected by means of switches or relays arranged along a direct current bus, each relay being interposed between a battery terminal and a load terminal.
In such applications in the automotive sector, as in other application contexts, the aforesaid overcurrent problems, upon the closure of a connection, are particularly relevant.
In order to deal with such problems, devices and methods are known, which are suitable to implement a pre-charging function of the capacitances associated to the electrical loads, in order to limit the maximum circuit currents which could take place between the generator and the load itself.
Usually, such a pre-charge operation is carried out by means of ad hoc devices adapted to equalize the charge voltage to the generator voltage by means of a limited current charge of the capacitance associated to the load. In other terms, the pre-charge operation aims at reducing the difference between the voltages of the load and of the generator, before their connection, below an appropriately defined threshold level. Such pre-charge devices are usually external with respect to the relay.
In some more advanced known solutions, a pre-charge circuit is associated to the relay and/or integrated thereto. However, also such solutions require the presence of complex external control and diagnosis systems.
In this regard, it is worth noting that the pre-charge function requires a check of the correct result of the occurred electrical pre-charging. Indeed, the absence of such a check would make the protection guarantee offered by pre-charging uncertain, and ultimately would thwart the advantages thereof.
The check of the correct pre-charge result must be based on a careful diagnosis of the operation of the relay and of the pre-charge circuit.
In the known solutions, such a check is normally performed by diagnosis circuits/systems, external to the relays, which must be capable of acquiring high voltages and must be also electrically insulated with respect to the vehicle chassis.
So, in the aforesaid known solutions, even the more advanced ones in which there is a pre-charge circuit associated to the relay, problematic needs arise of having a complex and costly system of pre-charge acquisition, management and diagnosis and also the needs of making this system interoperate with each relay.
In light of the above, particularly in the context of automotive applications, but also in other application contexts, the need is strongly felt to have an electronic device with relays and pre-charge functions which is simple, highly integrated and capable of managing, concurrently with the interconnection operation of the circuit, also the related associated pre-charge and diagnosis operations and which, at the same time, is adapted to significantly reduce the weight and dimensions associated to the pre-charge and diagnosis devices.